1. Field of Invention
This invention relates to integrated circuit (IC) fabrication, and particularly to a method for forming patterns of dense conductor lines and their contact pads, and to a memory array having high density of conductor lines and contact pads.
2. Description of Related Art
The resolution in a photolithography process depends on the wavelength of the exposure light, the numerical aperture (NA) of the optical system and the design of the photomask, and has a limit of about ⅕ to ⅓ of the wavelength of the exposure light according to the exposure conditions. When the resolution required by an array of patterns exceeds the resolution of the lithographic system, for example, in a case of forming the gate line array of a high-density memory like a DRAM of next generation, a pitch reduction method is needed, mainly based on the spacer forming technique.
For example, patterns of dense conductor lines beyond lithographic resolution can be formed as follows. Parallel base line patterns are lithographically defined and trimmed, linear spacers having a smaller width/pitch and a double number are formed on the sidewalls of the base line patterns, and then the base line patterns are removed, leaving the linear spacers as the target line patterns beyond the lithographic resolution.
To lithographically define contact pads at the ends of the small-pitch conductor lines, a so-called “shark-jaw” layout is conventionally used for the line ends, wherein the line ends of each pair of neighboring lines form a “loop” that is shifted from each neighboring loop and is large in length and width to provide sufficient spaces for the formation of the respective contact pads of the respective conductor lines. Each loop is then opened by etching to separate the corresponding two neighboring lines, and then contact pads are formed around the end portions of the opened loops.
However, the shark jaw layout takes much lateral area so that the integration degree of the devices is adversely affected. Moreover, definition of the contact pads requires an additional lithography process.